Electronically controllable brake operating system

ABSTRACT

An electronically controllable brake actuation system for automotive vehicles includes a simulator interacting with the master brake cylinder, a pressure source drivable by an electronic control unit and by which wheel brakes of the vehicle are pressurizable, the wheel brakes being connectable to the master brake cylinder by at least one hydraulic connection that is closable by separating valves, a device for the identification of the driver&#39;s wish for deceleration, each one inlet and outlet valve connected upstream of the wheel brakes, and wheel sensors sensing the rotational behavior of the vehicle wheels. 
     To improve the meterability of braking pressure of a system of the above type, especially in the range of low pressure values, the pressure source is configured as at least one continuously adjustable piston-and-cylinder assembly having a pressure chamber which is connectable to the master brake cylinder and the wheel brakes.

BACKGROUND OF THE INVENTION

The present invention relates to an electronically controllable brakeactuation system.

A brake actuation system of this type is disclosed in German patentapplication No. 31 24 755. The pressure source of the prior art brakeactuation system includes a pump, a hydraulic accumulator and a pressurefluid supply reservoir. The function of the separating valves and theinlet and outlet valves is performed by multi-position valves orfour-way/four-position directional control valves having inlet portswhich are connected to the pressure side of the pump or the accumulator,the pressure fluid supply reservoir and each one pressure chamber of thedual-circuit master brake cylinder. The wheel brakes are connected tothe outlet ports. During independent braking or pressure increase, thefour-way/four-position directional control valve is switched to itsfirst operating position where the wheel brakes are separated from themaster brake cylinder and connected to the pressure source. A phasewhere the pressure is maintained constant is achieved in a secondoperating position where the wheel brakes are isolated from the masterbrake cylinder and from the pressure source. Pressure decrease iseffected in a third operating position where a connection is providedbetween the wheel brakes and the unpressurized pressure fluid supplyreservoir.

Apart from the comparatively high costs incurred by the use of thesophisticated pressure source, the meterability of braking pressure inthe prior art brake actuation system is a disadvantage, especially inthe low-pressure range, which is due to the use of thefour-way/four-position directional control valves.

Therefore, an object of the present invention is to improve upon anelectronically controllable brake actuation system of theabove-mentioned type to such effect as to virtually eliminate theshortcomings mentioned with respect to ABS control. More particularly,the objective is to considerably improve the meterability of brakingpressure in the low-pressure range and to additionally reduce the totaleffort and structure.

SUMMARY OF THE INVENTION

According to the present invention, this object is achieved because thepressure source is configured as at least one continuously adjustablepiston-and-cylinder assembly having a pressure chamber which isconnectable to the master brake cylinder and the wheel brakes. It isachieved by these provisions that normal braking operations are carriedout similarly by way of the piston-and-cylinder assembly, and thepressure-retaining phases are achieved in an energy-saving way byoperation of the normally open (NO) inlet valves. The speed of brakingpressure increase can be augmented by a retarded operation of theseparating valves.

The present invention will be explained in detail in the followingdescription of three embodiments, making reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a wiring diagram of a first design of the brake actuationsystem of the present invention;

FIG. 2 is a wiring diagram of a second design of the brake actuationsystem of the present invention; and

FIG. 3 is a wiring diagram of a third design of the brake actuationsystem of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The electronically controllable brake actuation system of the presentinvention shown in the drawings includes a dual-circuit master brakecylinder or tandem master cylinder 2 operable by an actuating pedal 1.The tandem master cylinder 2 has pressure chambers 5, 6 separated fromeach other, confined by two pistons 3, 4 and being in connection to anunpressurized pressure fluid supply reservoir 30. The first pressurechamber (primary pressure chamber) 5 is connected to a first pressurechamber 10 of a piston-and-cylinder assembly 9 by way of a closablefirst hydraulic line 11. For example, a wheel brake 7 associated withthe front axle and a wheel brake 8 associated with the rear axle areconnected to the assembly 9 which preferably has a dual-circuitconfiguration. Line 11 is closed by way of a first separating valve 16.An electromagnetically operable, preferably normally open (NO) inletvalve 12, 13 is inserted into each of the line portions between thepressure chamber 10 and the wheel brakes 7, 8. Further, a low-pressureaccumulator 36 is connected to the pressure chamber 10 by way of anon-return valve 17 which opens towards the pressure chamber 10.Accumulator 36 is connectable to the wheel brakes 7, 8 by way of eachone electromagnetically operable, preferably normally closed (NC) outletvalve 14, 15.

The second pressure chamber 6 of the master brake cylinder 2, to which apressure sensor 18 can be connected, is connected to a second pressurechamber 20 of the piston-and-cylinder assembly 9, on the one hand, andto the other pair of wheel brakes (not shown), on the other hand, by wayof a hydraulic line 25 which is closable by a second separating valve19. Because the configuration of the hydraulic circuit connected to thesecond pressure chamber 6 of the master brake cylinder 2 is identicalwith the circuit described with respect to the first brake circuit 11,there is no need for discussing it in the following text.

The above-mentioned piston-and-cylinder assembly 9 which is used as anindependent assist pressure source, in turn, includes a tandem-designhydraulic cylinder 21, wherein two pistons 22, 23 are slidable whichconfine the above-mentioned pressure chambers 10, 20. The first piston22 is drivable by a preferably reversible direct-current motor 24.

An electronic control unit 26 is used for the joint actuation of thedirect-current motor 24 and the electromagnetic valves 12 to 15, 16 and19. Output signals of an actuating travel sensor 29, interacting withthe actuating pedal 1, and of the above-mentioned pressure sensor 18 aresent as input signals to the control unit 26, the signals permittingidentification of the driver's wish for deceleration. However, othermeans, such as a force sensor sensing the actuating force on theactuating pedal 1, may also be used for the identification of thedriver's wish for deceleration. Output signals of wheel sensors,representative of the driving speed of the vehicle, are sent as furtherinput variables to the electronic control unit 26. The wheel sensorsassociated with the wheel brakes 7, 8 have been assigned referencenumerals 27, 28. Further, there is provision of anangle-of-rotation/voltage converter 31 which senses the angular positionof the rotor of the d-c motor 24 and thereby permits indirectlydetermining the position of the pistons 22, 23 of thepiston-and-cylinder assembly 9.

As can be seen in the embodiment of FIG. 1, a simulator 32 is interposedin terms of effect between the actuating pedal 1 and the master brakecylinder 2. Simulator 32 includes a sleeve 33, which is in aforce-transmitting connection to the actuating pedal 1 and forms acomponent of the first master cylinder piston 3, and a simulator spring34 arranged inside the sleeve 33. The simulator spring 34 is axiallysupported on the piston 3, on the one hand, and on the sleeve 33, on theother hand.

The operation of the brake actuation system shown in the embodiment ofFIG. 1 in the drawing is as follows: when a braking operation isinitiated by depression of the brake actuating pedal 1, the actuatingcondition is identified by the actuating travel sensor 27 and advised tothe electronic control unit 26. Control signals of control unit 26 causechange-over of the valves 16 and 19 and, thereby, separation of themaster cylinder pressure chambers 5, 6 from the pressure chambers 10, 20of the piston-and-cylinder assembly 9. The driver's wish fordeceleration is signalled a second time by the pressure sensor 18, or asecond preset standard of an actual pressure value is sent to theelectronic control unit 26 which produces actuating signals for the d-cmotor 24. Motor 24 initiates displacement of the pistons 22, 23 in theactuating direction and, thus, pressure increase in the wheel brakes 7,8, 7′, 8′. The adjustment of nominal values and actual values isperformed by a second pressure sensor 35 which is connected to the firstpressure chamber 10 of the piston-and-cylinder assembly 9. The usualpedal feel which can be sensed by the driver during a braking operationis ensured by the compression of a simulator spring 34.

Pressure is reduced by the return movement of the pistons 22, 23,possibly by an active reversal of the direction of rotation of thedirect-current motor 24.

An excessive volume of pressure fluid can be stored in the low-pressureaccumulators 36 in ABS control operations. In the wheel beingcontrolled, pressure variation occurs by way of the inlet and outletvalves 12, 13 and 14, 15, respectively, and the low-pressure accumulator36 can be evacuated by way of the non-return valve 17 due to theresetting movement of the piston-and-cylinder assembly 9.

The separating valves 16, 19 are closed in a traction slip controloperation or a driving stability control operation. The necessarybraking pressure is generated by the piston-and-cylinder assembly 9. Apressure-retaining phase is achieved by change-over of the (NO) inletvalve 12 or 13. The pressure can be decreased by change-over of thenormally closed (NC) outlet valve 14, 15 or by operation of the closed(NC) inlet valve 12, 13 and a simultaneous reduction of the currentdelivered to the d-c motor 24. The above-mentioned non-return valve 17permits a return flow of the pressure fluid in the direction of thepiston-and-cylinder assembly 9 after or even during control.

In the second and third embodiment of the object of the presentinvention shown in FIGS. 2 and 3, two one-circuit piston-and-cylinderassemblies 109 ₁₁, 109 ₂₁, 109 ₁₂, 109 ₂₂ are used instead of thedual-circuit piston-and-cylinder assembly 9 mentioned with respect toFIG. 1. The pressure chambers 110 ₁₁, 110 ₁₂ and, respectively, 120 ₂₁,120 ₂₂ of the one-circuit piston-and-cylinder assemblies are connectedto the pressure chambers 5, 6 of the master brake cylinder 2 by way ofthe separating valves 16, 19, on the one hand, and to each one pair ofwheel brakes, on the other hand.

The allotment of the brake circuits of the second embodiment shown inFIG. 2 corresponds to the brake circuit allotment of the firstembodiment shown in FIG. 1 so that each one wheel brake 7, 8, 7′, 8′associated with the front axle and the rear axle cooperates with eachpressure chamber 110 ₁₁, 120 ₂₁ of the piston-and-cylinder assembly 109₁₁, 109 ₂₁. Preferably, a differential-pressure/voltage converter 36 isconnected between the two pressure chambers 110 ₁₁, 120 ₂₁.

Preferably, the brake circuit allotment of the third embodiment shown inFIG. 3 is chosen so that the wheel brakes 108, 108′ associated with therear axle of the vehicle are connected to the pressure chamber 110 ₁₂ ofthe first piston-and-cylinder assembly 109 ₁₂, the wheel brakes beingconnected to the pressure chamber 110 ₁₂ without the intermediary of theinlet and outlet valves. The wheel brakes 107, 107′ associated with thefront axle are connected to the pressure chamber 120 ₂₂ of the secondpiston-and-cylinder assembly 109 ₂₂ by way of each one inlet valve (112,113) and one outlet valve (114, 115) (black-and-white circuit split-up).Another brake circuit allotment (diagonal split-up) is permitted byusing an electromagnetically operable, normally closed (NC) valve 37which is preferably interposed between the second separating valve andthe pressure chamber 120 ₂₂ of the second piston-and-cylinder assembly109 ₂₂.

The present brake system is also appropriate for the recuperation ofbrake energy in electric vehicles. In this case, the piston-and-cylinderassembly is actuated in the delay control circuit which also takes intoaccount the effect of the brake torque produced by the vehicle drive.When the total torque which can be transmitted to the front axle isexceeded, the NO-valves are being closed and the braking pressure on therear axle increased until the optimal brake force distribution isreached.

What is claimed is:
 1. An electronically controllable brake actuationsystem for automotive vehicles with a plurality of wheels, which systemincludes a pedal-actuated master brake cylinder, a simulator interactingwith the master brake cylinder, a plurality of wheel brakes connectableto the master brake cylinder by at least one hydraulic connection thatis closable by a separating valve, a pressure source that is actuatableby an electronic control unit and by which the wheel brakes arepressurizable, a device for the identification of characteristics of apedal actuation, wherein the pressure source is configured as at leastone continuously adjustable piston-and-cylinder assembly having at leastone pressure chamber to which preselected ones of the wheel brakes areconnected by an intermediary of inlet valves, wherein the at least onepiston-and-cylinder assembly is provided by at least one hydrauliccylinder having a piston which is operable by a reversibledirect-current motor, wherein the pressure chamber of the at least onepiston-and-cylinder assembly is connected to a low-pressure accumulatorby way of a non-return valve which opens towards the pressure chamber,the preselected wheel brakes being connectable to the accumulator by wayof an outlet valve, wherein the inlet valve is configured as anelectromagnetically operable, normally open control valve, and theoutlet valve is configured as an electromagnetically operable, nonnallyclosed control valve, wherein the pressure source is configured as afirst and a second continuously adjustable one-circuitpiston-and-cylinder assembly, each having a pressure chamber to whichwheel brakes, each associated with a first or a second vehicle axle, areconnected, wherein a normally closed valve is inserted into theconnection between the wheel brakes associated with the first vehicleaxle and the first piston-and-cylinder assembly, whereas the connectionbetween the wheel brakes associated with the other vehicle axle iswithout an intermediary of switching valves.
 2. An electronicallycontrollable brake actuation system as claimed in claim 1, wherein thereis a provision of a sensor which senses the travel of the piston.
 3. Anelectronically controllable brake actuation system as claimed in claim1, wherein the pressure accumulator is disposed in communication withsaid at least one piston-and-cylinder assembly and at least one inletvalve.
 4. An electronically controllable brake actuation system asclaimed in claim 1, wherein the master brake cylinder is operable by anactuating pedal, wherein the device for identifying the characteristicsof a pedal actuation is provided by the combination of a travel sensor,which senses the actuating travel of the actuating pedal, and a pressuresensor which senses the hydraulic pressure that develops in the masterbrake cylinder.
 5. An electronically controllable brake actuation systemas claimed in claim 1, wherein the master brake cylinder is operable byan actuating pedal and the simulator is provided by a compression springwhich is arranged in terms of effect between the actuating pedal and themaster brake cylinder.
 6. An electronically controllable brake actuationsystem as claimed in claim 1, wherein the device for identifying thecharacteristics of a pedal actuation is provided by two pressure sensorswhich each are connected to one pressure chamber of the master brakecylinder.
 7. An electronically controllable brake actuation system asclaimed in claim 1, wherein a means is provided to sense the position ofthe at least one piston of the at least one piston-and-cylinderassembly.
 8. An electronically controllable brake actuation system asclaimed in claim 1, wherein there is provision of a pressure sensorwhich senses the hydraulic pressure generated by the at least onepiston-and-cylinder assembly.
 9. An electronically controllable brakeactuation system as claimed in claim 1, wherein a pressure switch isinterposed between the master cylinder and the at least onepiston-and-cylinder assembly.